Volvox in South Africa. 555 



spicuous constituent of the cells in the anterior part of the coenobium 

 (fig. 1, A, B). Situated in the dorsal strap-shaped prolongation of 

 the chloroplast symmetrically beneath the points of insertion of the 

 cilia (fig. 1, D), the eyespot is easily distinguished under comparatively 

 low powers by its bright orange-red colour and high refraction, and 

 since it remains unaltered both in size and colour as the cell ages, 

 while the chloroplast grows smaller and paler, it is even more con- 

 spicuous in old than in young colonies. 



Viewed from the front or back of the cell it appears as a circular 

 disc 1-5-2-2 fj., most often 2 /x, in diameter. More often it is seen 

 in side view. It is a lenticular structure, convex towards the inside 

 of the cell, i.e. on its anterior side, concave at the back (fig. 1, A, B, 

 D ; Plate XXXVIII, D). 



Towards the equator of the colony the eyespots become smaller, 

 usually disappearing completely as pigmented spots in the posterior 

 quadrant. As a rule, however, even in these cells a small, highly 

 refractive granule may be distinguished, which, although it contains 

 no haematochrome, probably represents a vestigial eyespot, since it 

 occupies the position of that organ. 



As in the case of the cilia, the position of the eyespot has a definite 

 orientation in relation to the axis of the colony, always occupying 

 a position between the points of insertion of the cilia, but well below 

 them, in the upper part of the chloroplast on the dorsal side of the 

 cell, i.e. facing in the direction of the anterior pole (Plate XV, A ; 

 Plate XIX, A). Its position in relation to the apex of the cell appears 

 to depend somewhat on the position of the cell in the colony. At 

 the anterior pole it is often rather low down in the cell, rather higher 

 further back in the colony. 



The photograph shown in fig. D, Plate XXXVIII, was taken from 

 a colony of V. capensis, from one of the Belvedere Road vleis at 

 Claremont (Cape Flats). The living colony was lying on the slide 

 with its anterior pole upwards, so that it was possible to focus down 

 directly on to the pole, which lies practically in the centre of the 

 photo. The objective (1-9 mm. oil immersion) was focussed down 

 on to the plane in which the eyespots lie, just below the insertion of 

 the cilia and thus well above the protoplasmic connections, which 

 consequently do not show at all. The eyespots, as seen from above, 

 show well, as do the walls of the cells. The outline of the protoplast 

 is not very sharp, but sufficiently clear for the position of the eyespot 

 in the cell to show, and the shape of the latter as seen in optical cross- 

 section shows very clearly in some of the cells. 



